Rotary hydraulic machines of the subject type generally include a housing, a rotor mounted for rotation within the housing, and a plurality of vanes individually slidably disposed in corresponding radially extending peripheral slots in the rotor. A cam ring radially surrounds the rotor, and has an inwardly directed surface forming a vane track and one or more fluid pressure cavities between the cam surface and the rotor. Inlet and outlet passages feed hydraulic fluid to and from the cavities. Fluid inlet and outlet ports are positioned at circumferentially spaced edges of the fluid cavities.
It is desirable to match fluid displacement in machines of the subject type to operating characteristics of the system with which the machine is to be associated. For example, maximum displacement of a vane-type fuel pump is coordinated with maximum fuel requirements of the associated engine application. However, system requirements typically vary with operating conditions, so that a fixed displacement machine designed as a function of the most demanding operating conditions may function with less than desired efficiency under other operating conditions. In the exemplary case of a fuel pump, fuel flow requirements under engine starting conditions greatly exceed requirements during normal operation. It has heretofore been proposed to provided relatively complex and expensive valving arrangements (flow or fuel controls) at the pump outlet to meter a portion of the pump output to the engine as a function of engine demand, while returning the remainder to the pump inlet causing fuel heating from the throttling effects.
A general object of the present invention, therefore, is to provide a rotary hydraulic machine of the subject type in which effective machine displacement can be controlled as a function of demand, and yet is inexpensive to manufacture and assemble as compared with variable-displacement rotary hydraulic machines of the prior art. Another object of the present invention is to provide a machine of the described character that is compact in assembly. A further and more specific object of the invention is to provide a split-discharge balanced duallobe vane-type machine design that may be employed as a pump, motor, flow divider, pressure intensifier or the like with minimum modification to overall design principles and components.